Girls who are obese at the age of four are significantly more likely to hit puberty before their 10th birthday, according to research which predicts that puberty will come earlier in the UK as the child obesity crisis worsens.

The study is the first to track children from when they were toddlers to aged 12, and to establish a firm link between childhood obesity and early onset puberty.

The findings will add to pressure on the government to tackle the rising rates of child obesity.

The American researchers warn that the obesity crisis is now affecting children's development, while British experts say that the trend will follow in the UK as childhood obesity reaches US levels.

"We have to understand that we're catching up with the States - there's a very small window in which we can do something about this," said David Haslam, clinical director of the National Obesity Forum. "This is further proof that obesity disrupts hormones through people's lives, right through from early childhood to menopause."

Joyce Lee, assistant professor in paediatric endocrinology at the University of Michigan, and lead researcher on the study, said: "This is a crucial study because it is the first longitudinal study to follow girls from 36 months to the age of 12. We witnessed early onset puberty at nine among those who were obese by the age of four. Before it's not been clear whether girls are obese because they are hitting puberty earlier or hitting puberty early because they are obese.

"Early puberty is associated with increased psychological and social problems, early alcohol consumption and smoking. There can be long-term implications for the children."

The research, published in the American journal Pediatrics, studied 400 girls, recording weight and early signs of puberty, through observation and with interviews with the mothers. The monitoring included breast development and the start of menstruation. About 30% of the children were overweight or obese at the age of nine.

Scores at all ages of a higher body mass index (BMI), the calculation of weight using height measurements, were found to have a strong association with an earlier onset of puberty in girls. For every extra point on the girls' BMI scores at 36 months the odds of having earlier puberty increased by 44%.

The study says: "Earlier onset of puberty in girls has been associated with a number of adverse outcomes, including psychiatric disorders and deficits in psychosocial functioning, earlier initiation of alcohol use, sexual intercourse and teenage pregnancy and increased rates of adult obesity and reproductive cancers."

Dr Lee said: "Beyond identifying how obesity causes early puberty, it's also important to determine whether weight control interventions at an early age have the potential to slow [its] progression."

Figures from 2004, from the International Obesity Taskforce, a global think-tank which works with the World Health Organisation, suggest that the level of obesity among English boys has already caught up with American boys, with 31.7% being overweight and about 10% clinically obese. For girls the figures are higher but British girls are still two to four years behind Americans.

The Department of Health's own research suggests that a fifth of all children under 15 will be clinically obese by 2010, matching American levels of obesity in 2000. The proportion of clinically obese children in English secondary schools doubled in a decade.

Pressure is mounting on the government to tackle the issue as it has become clear it is likely miss its target of halting the rise in childhood obesity by 2010.

Craig Williams, associate director of the Children's Health and Exercise Research Centre at the University of Exeter, said other studies had suggested it was not just the obesity that could prompt puberty, but also lack of exercise.

"We know that obesity trends are following the US. There's no reason why the mechanisms that mean obese children hit puberty earlier should be different in different countries and it's not just obese children that might be affected but children who are inactive. Previous research showed that puberty moved forward by a third of a year every decade from 1880 to 1960. That move has been stabilising, but this research suggests it could get earlier in the future."